I was with the same problem, Angular 4 'ng' is not recognized in Windows 10. Now I discovered a working solution. After successful installation of node and angular CLI do the following steps.
As we know after node we have to run following command for angular/cli (Angular 4)
npm install -g @angular/cli
-g stands for global in your machine.
Open C:\usr\local and copy the path or the path where angular CLI located on your machine, as below image:
Now search for 'Environment Variable' in your Windows, and add copied path in the following location:
Now open environment variable in your Windows, and add copied path in the following location:
Advanced > Environment Variable > User Variables and System Variables
As below image:
That's all, now open your command prompt and try with any 'ng' command, for example, create a new angular app as below image.
Let me know if above method solved your issue for Angular 4 'ng' is not recognized in Windows 10.